1. Technical Field
The present invention relates to a method for forming transcriptional circuits and a method for manufacturing a circuit board.
2. Description of the Related Art
Developments in the electronics industry have promoted smaller and more functionalized electronic parts, including mobile phones, etc., and as a result, there is a growing demand for smaller and higher-density printed circuit boards. According to such trends towards lighter, thinner, and simpler electronic products, so also is the printed circuit board being endowed with finer patterns, smaller sizes, and packaged forms.
A technique currently in wide use for manufacturing fine circuit patterns is photolithography, which is a method of forming patterns on a board coated with a thin film of photoresist. However, the sizes of patterns thus formed are limited by the optical diffraction phenomenon, and the resolving power is almost proportional to the wavelengths of the rays used. Therefore, with greater degrees of integration of semiconductor components, an exposure technique is required that uses shorter wavelengths for forming fine patterns, but such a method is liable to cause non-uniformity in the critical dimensions of a photoresist pattern, so that the circuit pattern formed using the photoresist pattern as a mask may turn out to have a different form from that initially desired. There may also be a problem that impurities occurring during the processes can react with and erode the photoresist, so that the photoresist pattern may change.
Processes such as MSAP (modified semi-additive process), SAP (semi-additive process), etc., have been used as methods of implementing high densities for fine-line circuit patterns, in which circuits are selectively grown on a thin copper film. However, there are difficulties in applying these methods, due to the additional infrastructure required in terms of materials and investments for new equipment, and because damage may occur on the finished circuits during the procedures for removing portions of the thin copper film that are not used as circuits, so that the target circuit width is not obtained.
Furthermore, the circuit patterns formed according to such methods are exposed at the upper portion of the insulation board, so that the overall height of the board is great, and undercuts can occur at the attachment portions between the circuit patterns and the insulation board, causing the circuits to be peeled off from the insulation board.